A proposal to amend part 39 of the Federal Aviation Regulations to include an airworthiness directive (AD) that is applicable to certain Boeing Model 757 series airplanes was published in the Federal Register on September 8, 1993 (58 FR 47225). That action proposed to require tests of the thrust reverser system, and repair, if necessary; installation of a modification that would terminate those tests; and repetitive operational checks of that installation, and repair, if necessary. \n\n\tInterested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the comments received. \n\n\tOne commenter supports the proposed rule. \n\n\tSeveral commenters question the requirement for periodic operational checks of the sync- lock following its installation, as specified in paragraph (c) of the proposal: \n\n\t1.\tThe Air Transport Association (ATA) of America, on behalf of its members, states that, while ATA members are not opposed to accomplishing the proposed checks as part of their maintenance programs, these members are opposed to accomplishing the checks as part of the requirements of an AD. The commenters believe that the requirement for operational checks is equivalent to issuing a Certification Maintenance Requirements (CMR) item by means of an AD. \n\n\tATA adds that, if the FAA finds sufficient justification to include the requirement for operational checks in the AD, an alternative to accomplishment of the checks should be provided in the final rule. ATA reasons that an alternative is justified because no data exist to show that repetitive checks of a modified thrust reverser cannot be handled adequately through an operator's maintenance program. The suggested alternative follows: Within 3 months after accomplishing the sync-lock installation, revise the FAA-approved maintenance inspection program to include an operational check of the sync-lock. The initial check would be accomplished within 1,000 hours time-in-service after modification. The AD would no longer be applicable for operators that have acceptably revised the maintenance program. Operators choosing this alternative could use an alternative recordkeeping method in lieu of that required by Federal Aviation Regulation (FAR) 91.417 or 121.380. The FAA would be defined as the cognizant Principal Maintenance Inspector (PMI) for operators electing this alternative. \n\n\t2.\tOne commenter, Boeing, requests that the proposed requirement for operational checks be removed from the AD until the FAA reviews the "more comprehensive" scheduled maintenance recommendations developed by the Model 757/767 Thrust Reverser Working Group, which will be recommended in the next revision to the Maintenance Review Board (MRB) report. Boeing believes that adoption of the maintenance recommendations contained in that forthcoming revision will ensure that an adequate level of safety (with regard to the sync-lock installation) will be maintained by all operators of Model 757 series airplanes. \n\n\t3.\tOne commenter states that these checks should not be required because failures of the sync-lock would not be hidden. The commenter states that normal operation of the thrust reverser will indicate if the sync-lock system is active, and whenever the sync-lock system is not available, either the unlock indicator on the external surface of the engine cowling will indicate this condition or the thrust reverser will not deploy on request. \n\n\t4.\tOne commenter asks why operational checks would be required at more frequent intervals following installation of an additional safety feature than prior to its installation. \n\n\tThe FAA recognizes the concerns of these commenters regarding the requirement for periodic operational checks of the sync-lock following its installation. However, the FAA finds that the operational checks are necessary in order to provide an adequate level of safety and to ensurethe integrity of the sync-lock installation. The actions required by this AD are consistent with actions that have been identified by an industry-wide task force as necessary to ensure adequate safety of certain thrust reverser systems installed on transport category airplanes. Representatives of the Aerospace Industries Association (AIA) of America, Inc., and the FAA comprise that task force. Representatives from other organizations, such as ATA, have participated in various discussions and work activities resulting from the recommendations of the task force. \n\n\tThe FAA acknowledges that the operational checks specified in this AD and CMR items are similar in terms of scheduled maintenance and recordkeeping. This AD addresses an unsafe condition and requires installation of the sync-lock to correct that unsafe condition. The FAA has determined that the requirement for operational checks is necessary in order to ensure the effectiveness of that installation in addressing the unsafe condition. This determination is based on the fact that the sync-lock is a new design whose reliability has not been adequately proven through service experience. In addition, service experience to date has demonstrated that failures can occur within the sync-lock that may not be evident during normal operation of the thrust reverser system and may not result in activation of the sync-lock "unlock" indicator. The ATA's suggested alternative to accomplishment of the operational checks would permit each operator to determine whether and how often these checks should be conducted. In light of the severity of the unsafe condition, however, the FAA has determined that allowing this degree of operator discretion is not appropriate at this time. Therefore, this AD is necessary to ensure that operators accomplish checks of the integrity of the sync-lock installation in a common manner and at common intervals. \n\n\tThe FAA also finds that addressing operational checks of the sync-lockintegrity in a recommended action, such as an MRB report, will not ensure an acceptable level of safety with regard to the thrust reverser system. However, the FAA recognizes that an operational check interval of 4,000 hours time-in-service, which will be recommended by Boeing for inclusion in the next revision to the MRB report, corresponds more closely to the interval at which most of the affected operators conduct regularly scheduled "C" checks. The FAA has reconsidered the proposed interval of 1,000 hours time-in-service for accomplishment of repetitive operational checks. In light of the safety implications of the unsafe condition addressed and the practical aspects of accomplishing orderly operational checks of the fleet during regularly scheduled maintenance where special equipment and trained maintenance personnel will be readily available, the FAA finds that accomplishment of the checks at intervals of 4,000 hours time-in- service will provide an acceptable level of safety.Paragraph (c) of the final rule has been revised accordingly. \n\n\tBoeing requests that specific references to page numbers and revision dates of the Boeing 757 Airplane Maintenance Manual (AMM) be eliminated from paragraphs (a)(1), (a)(2), (c)(1), and (c)(2) of the AD. Boeing recommends that the proposed AD specify only the ATA Chapter-Section- Subject pageblock title and task title in these paragraphs. A second commenter states that the referenced pages could not be found in its latest copy of the AMM. \n\n\tBoeing explains that the AMM's are customized for each operator to reflect all of the equipment in that operator's fleet. Therefore, the number of pages for any given procedure is variable, depending on the number of different equipment configurations documented in an operator's AMM. Boeing also indicates that AMM procedures are revised periodically for non- technical reasons. Boeing adds that changes to the structure of the procedures are necessary to accommodate an upgrade of the publishing system that is currently under way, which, in addition to repagination, will necessitate the issuance of revised AMM pages. \n\n\tBoeing states that the effect of specifying AMM page numbers and revision dates in the AD is that operators may be unable to use the procedure contained in the AMM to perform certain tests required by the AD. Each operator would be required to maintain an obsolete version of the procedure, or to request FAA approval of an alternative method of compliance with the AD that would allow the use of the current version of the AMM. \n\n\tThe FAA concurs partially. In light of the information submitted by the commenter, the FAA finds that specific AMM page numbers and dates should not be specified in the final rule. Therefore, such references have been removed from paragraphs (a)(1) and (a)(2) of the final rule. However, for those paragraphs, the FAA does not agree that copies of the specific procedures should be included in the final rule. Therefore, paragraphs (a)(1) and (a)(2) of the final rule have been revised to cite only the appropriate section and task title specified in the AMM for accomplishment of the tests required by those paragraphs. \n\n\tThe FAA's objective in proposing periodic operational checks of the sync-lock device, as specified in paragraph (c) of this AD, is to ensure the integrity of the locking function. However, subsequent to the issuance of the proposal and the receipt of Boeing's comments to the proposal, Boeing has submitted to the FAA separate procedures for accomplishment of the operational check of the sync-lock integrity. These procedures have been defined in paragraph (c) of the final rule; therefore, the AMM references specified in paragraph (c) of the NPRM have been removed from the final rule. Additionally, the procedures for the operational checks are accomplished independently of the other thrust reverser system tests specified in paragraph (c) of the proposal. Accordingly, the FAA has revised paragraph (c) of the final rule to require periodic accomplishment of operational checks of the sync-lock integrity only, and has removed the requirement for accomplishment of other tests specified in that paragraph of the proposal. \n\n\tSince the issuance of the proposed rule, Boeing has issued Revision 2 of Service Bulletin 757-78-0032, dated May 12, 1994. The service bulletin revision moves general work instruction Step B from Work Package 2 to Step U in Work Package 8. In Revision 1 of the service bulletin, Step B of Work Package 2 specified procedures for removal of the ground to the EICAS for the REV ISLN VAL message; however, the ground should not be removed as part of Work Package 2. Rather, the ground should be removed as part of Work Package 8 in order to avoid loss of the REV ISLN VAL message on EICAS. Revision 2 of the service bulletin correctly describes procedures for removal of the ground as part of Work Package 8. Revision 2 of the service bulletin also describes procedures for installation of an additional bracket on the P36 disconnect bracket and to make a cutout on the P37 disconnect bracket on certain airplanes. \n\n\tThe FAA has reviewed and approved this latest revision to the service bulletin and has revised the final rule to reflect it as the appropriate source of service information. The FAA finds that citing this latest revision to the service bulletin will impose no additional burden on any operator. \n\n\tIt should be noted that Revision 2 of Boeing Service Bulletin 757-78-0032 references Rolls- Royce Service Bulletins RB.211-78-9627 and RB.211-78-9613 as additional sources of service information for accomplishment of the originally proposed sync-lock installation. However, the Boeing service bulletin does not specify the appropriate revision levels for the Rolls-Royce service bulletins. Therefore, the FAA has added "NOTE 1" to paragraph (b) of this AD to specify that the intent of that paragraph is that the appropriate revision levels for the Rolls-Royce service bulletins that are to be used in conjunction with Boeing Service Bulletin 757-78-0032 are as follows: Rolls- Royce Service Bulletin RB.211-78-9613, dated December 3, 1992, or Revision 1, dated March 5, 1993, or Revision 2, dated October 1, 1993; and Rolls-Royce Service Bulletin RB.211-78-9627, dated December 3, 1992. \n\n\tIn addition, since the issuance of the proposed rule, Rolls-Royce has issued Service Bulletin RB.211-78-9822, dated October 1, 1993. This service bulletin describes procedures for installation of a revised thrust reverser sync-lock. The FAA has determined that accomplishment of the actions described in this service bulletin, in conjunction with Boeing Service Bulletin 757- 78-0032 (which was cited in paragraph (b) of the proposal as the appropriate source of service information for installation of an additional thrust reverser system locking feature), constitutes an acceptable alternative to the sync-lock installation specified in paragraph (b) of the proposal. \n\n\tIn light of this information, paragraph (b) of the final rule has been revised to include paragraph (b)(1), which contains the requirement for installation of an additional thrust reverser system locking feature that was specified in the proposed rule, and paragraph (b)(2), which provides for installation of a revised thrust reverser sync-lock as an acceptable alternative to paragraph (b)(1) of this AD. Accomplishment of the revised installation specified in paragraph (b)(2) requires no additional work hours beyond the 506 work hours specified in the economic impact information, below, for accomplishment of the originally proposed sync-lock installation. \n\n\tAdditionally, it should be noted that Rolls-Royce Service Bulletin RB.211-78-9822 references Rolls-Royce Service Bulletin RB.211-78-9613 as an additional source of service information for airplanes equipped with Rolls-Royce RB211-535E4/E4B engines. Rolls-Royce Service Bulletin RB.211-78-9613 references Rolls-Royce Service Bulletin RB.211-78-9627 as an additional source of service information. However, the appropriate revision levels for these service bulletins are not specified in Boeing Service Bulletin 757-78-0032 or in any of the Rolls-Royce service bulletins. Therefore, the FAA has added "NOTE 2" to paragraph (b) of the final rule to specify that the appropriate revision levels to be used in conjunction with Rolls-Royce Service Bulletin RB.211-78-9822 are as follows: Rolls-Royce Service Bulletin RB.211-78-9613, Revision 2, dated October 1, 1993; and Rolls-Royce Service Bulletin RB.211-78-9627, dated December 3, 1992. \n\n\tAfter careful review of the available data, including the comments noted above, the FAA has determined that air safety and the public interest require the adoption of the rule with the changes previously described. The FAA has determined that these changes will neither increase the economic burden on any operator nor increase the scope of the AD. \n\n\tThere are approximately 250 Model 757 series airplanes of the affected design in the worldwide fleet. The FAA estimates that 95 airplanes of U.S. registry will be required to accomplish the restow and integrity tests required by this AD, that it will take approximately 1 work hour per airplane to accomplish those tests, and that the average labor rate is $55 per work hour. Based on these figures, the total cost impact of the AD on U.S. operators to accomplish each operational test is estimated to be $5,225, or $55 per airplane. \n\n\tThe FAA estimates that 95 airplanes of U.S. registry will be required to accomplish either modification specified in paragraphs (b)(1) and (b)(2) of this AD. It will take approximately 506 work hours per airplane to accomplish either of those modifications, and the average labor rate is $55 per work hour. Required parts will be supplied by the manufacturer at no cost to operators. Based on these figures, the total cost impact of the AD on U.S. operators to accomplish the modification is estimated to be $2,643,850, or $27,830 per airplane. \n\n\tThe FAA also estimates that 113 airplanes of U.S. registry will be required to accomplish the periodic operational tests of the sync-lock installation required by this AD, that it will take approximately 1 work hour per airplane to accomplish each test, and that the average labor rate is $55 per work hour. Based on these figures, the total cost impact of the AD on U.S. operators to accomplish each operational test is estimated to be $6,215, or $55 per airplane.\n \n\tBased on these figures, the total cost impact of the AD on U.S. operators is estimated to be $2,655,290. \n\n\tThe total cost impact figure discussed above is based on assumptions that no operator has yet accomplished any of the requirements of this AD action, and that no operator would accomplish those actions in the future if this AD were not adopted. \n\n\tThe FAA recognizes that the modification will require a large number of work hours to accomplish. However, the 5-year compliance time specified in paragraph (b) of this AD should allow ample time for the sync-lock installation to be accomplished coincidentally with scheduled major airplane inspection and maintenance activities, thereby minimizing the costs associated with special airplane scheduling. \n\n\tThe regulations adopted herein will not have substantial direct effects on the States, on the relationship between the national government and the States, or on the distribution of power and responsibilities among the various levels of government. Therefore, in accordance with Executive Order 12612, it is determined that this final rule does not have sufficient federalism implications to warrant the preparation of a Federalism Assessment. \n\n\tFor the reasons discussed above, I certify that this action (1) is not a "significant regulatory action" under Executive Order 12866; (2) is not a "significant rule" under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and (3) will not have a significant economic impact, positive or negative, on a substantial number of small entities under the criteria of the Regulatory Flexibility Act. A final evaluation has been prepared for this action and it is contained in the Rules Docket. A copy of it may be obtained from the Rules Docket at the location provided under the caption "ADDRESSES."\n\nList of Subjects in 14 CFR Part 39 \n\nAir transportation, Aircraft, Aviation safety, Incorporation by reference, Safety. \n\nAdoption of the Amendment \n\nAccordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration amends 14 CFR part 39 of the Federal Aviation Regulations as follows: PART 39 - AIRWORTHINESS DIRECTIVES \n\n1.\tThe authority citation for part 39 continues to read as follows: Authority: 49 U.S.C. App. 1354(a), 1421 and 1423; 49 U.S.C. 106(g); and 14 CFR 11.89. § 39.13 - (Amended) \n\n2.\tSection 39.13 is amended by adding the following new airworthiness directive: